Add photos and videos to Favourites on iCloud.com
When you add a photo or video to Favourites in Photos on iCloud.com, it is added to Favourites on any device with iCloud Photos turned on.
In Photos on iCloud.com, tap the Photos tab, then tap Select.
Tap the photos or videos you want to make a favorite, then tap at the top of the window.
To see your Favourites, tap the Albums tab, then tap Favourites in the All Photos & Favourites section.
If you want to remove a photo or video from Favourites, tap the photo or video, then tap the Favourites icon at the top of the window to deselect it. If you delete a photo or video from Favourites, it is deleted from Favourites on all your devices with iCloud Photos turned on.